Thm 3.9
Theorm 3.9 states that : two lines are perpendicular, then they intersect to form right angles.
perpendicular-lines.jpg
These lines intersect and form four right
angles. They are perpendicular lines.
MAGGIE RELLIHAN ^^

Thm 3.8 MEGHAN LEWIS AND ELENA FLORES
If two lines intersect to form a linear pair, of congruent angles then the lines are perpendicular.

A

http://stageometrych3.wikispaces.com/thm+3.8+thm+3.9+thm+3.63.9.pngB

If the two intersecting lines have two congruent right angles forming a linear pair (which they do it is just not labeled) then lines A and B are perpendicular.
THM 3.10 BY KAITLYN FIOLA
IF TWO SIDES OF TWO ADJACENT ACUTE ANGLES ARE PERPENDICULAR THEN THE ANGLES ARE COMPLEMENTARY.
3.10.gif
if line AB and line CB are perpendicular, then ABD and DBC are complementary.